Each year, millions of lab animals give their lives to improve, even save, the lives of humans.

The use of animals for biomedical research and chemical testing is a vast and, scientists say, vital enterprise. Treatment is regulated for only a small number of the animals — dogs, cats, monkeys and apes, hamsters, guinea pigs, rabbits, sheep, pigs and other farm animals, the creatures that people most relate to.

According to Scripps Howard News Service reporter Lee Bowman in "Animal Testing: Crucial or Cruel?," federal reports say that in a given year nearly 1 million regulated animals are used or awaiting use in experiments.

However, that number excludes an estimated 80 million to 100 million unregulated animals — rats and mice, mostly, but also birds, fish, reptiles and other life forms — used in lab testing annually.

The principal vehicle for regulation is the Animal Welfare Act, passed in 1966 in response to the scandalous trafficking in dogs, many of them stolen pets, for research purposes. The act applies to labs doing research on regulated animals and to labs doing research on unregulated species if it's done with federal funds.

The Public Health Service and the National Institutes of Health have some responsibility, but enforcement resides principally with the U.S. Department of Agriculture's Animal and Plant Health Inspection Service. As with many regulators, the service faces a daunting mandate: 150 inspectors for more than 12,000 facilities of all kinds, not just the 1,500 or so research labs. Given the state of the federal budget, help is not likely on the way.

Otherwise, the welfare of lab animals is subject to state and local laws, in-house rules and protocols and voluntary peer reviews by research associations. Still, animal-rights groups regularly turn up cases where lab animals have needlessly suffered or died.

These groups are conducting aggressive campaigns against animal testing, which they contend is cruel and unnecessary. And they seem to be having some impact. Public acceptance of animal testing has fallen recently from its historic levels of around 70 percent.

That has made research labs wary of publicity. As one biomedical researcher told Bowman, the industry needs to do a better job of explaining to the public "what we do and why we do it, as well as how much care we take of the animals."

Proponents argue that animal testing has played an essential role in every major advance in biology, medicine and cosmetics safety for the past century.

There is no clear answer to the moral dilemma of animal testing, only accelerated research and investment in alternatives and an industry adherence to the maxim of one respected researcher: "We wouldn't do it if we didn't have to do it."